Chemotherapeutic agents attenuate CXCL12-mediated migration of colon cancer cells by selecting for CXCR4-negative cells and increasing peptidase CD26.

BACKGROUND: Recurrence of colorectal cancer (CRC) may arise due to the persistence of drug-resistant and cancer-initiating cells that survive exposure to chemotherapy. Proteins responsible for this recurrence include the chemokine receptor CXCR4, which is known to enable CRC metastasis, as well as the cancer-initiating cell marker and peptidase CD26, which terminates activity of its chemokine CXCL12. METHODS: We evaluated the expression and function of CXCR4 and CD26 in colon cancer cell lines and xenografts following treatment with common chemotherapies using radioligand binding, flow cytometry, immunofluorescence, and enzymatic assays. RESULTS: 5-Fluorouracil, oxaliplatin and SN-38 (the active metabolite of irinotecan), as well as cisplatin, methotrexate and vinblastine, each caused decreases in cell-surface CXCR4 and concomitant increases in CD26 on HT-29, T84, HRT-18, SW480 and SW620 CRC cell lines. Flow cytometry indicated that the decline in CXCR4 was associated with a significant loss of CXCR4+/CD26- cells. Elevations in CD26 were paralleled by increases in both the intrinsic dipeptidyl peptidase activity of CD26 as well as its capacity to bind extracellular adenosine deaminase. Orthotopic HT-29 xenografts treated with standard CRC chemotherapeutics 5-fluorouracil, irinotecan, or oxaliplatin showed dramatic increases in CD26 compared to untreated tumors. Consistent with the loss of CXCR4 and gain in CD26, migratory responses to exogenous CXCL12 were eliminated in cells pretreated with cytotoxic agents, although cells retained basal motility. Analysis of cancer-initiating cell CD44 and CD133 subsets revealed drug-dependent responses of CD26/CD44/CD133 populations, suggesting that the benefits of combining standard chemotherapies 5-fluoruracil and oxaliplatin may be derived from their complementary elimination of cell populations. CONCLUSION: Our results indicate that conventional anticancer agents may act to inhibit chemokine-mediated migration through eradication of CXCR4+ cells and attenuation of chemokine gradients through elevation of CD26 activity.

Differential sensitivity to short-chain ceramide analogues of human intestinal carcinoma cells grown in tumor spheroids versus monolayer culture.

The cytotoxic activity of short-chain (C(2)) ceramide was evaluated in human intestinal carcinoma cells grown as multicellular tumor spheroids versus the same cells cultured as monolayers under closely comparable conditions. A decrease in cell number was seen in monolayer cultures of HT-29, Caco-2, and HRT-18 cells, with an EC(50) (concentration for half-maximal toxicity) of between 13 and 23 microM. However, when the same cells were grown in the multicellular spheroid format, C(2) was markedly less potent in reducing cell number, with an EC(50) of between 44 and 63 microM, representing a 1.9- to 4.9-fold decrease in its potency. The chemotherapeutic agents 5-fluorouracil and cisplatin were equally potent against spheroids and monolayer cultures, indicating that although drug access is a problem in conventionally grown tumor spheroids it is not a problem for spheroids grown under the conditions used in this study. Our results suggest that although ceramide is capable of inducing cell death in intestinal carcinoma cells grown in spheroid culture, its cellular toxicity is constrained by influences that are independent of drug access and may be the consequence of the altered cellular relationships. Carcinoma cell populations show an intrinsically decreased responsiveness to the effects of ceramide when they are grown in a three-dimensional culture format.